Photo: Spiral galaxy M101 (source: NASA).
The spiral galaxy looks like a rotating spiral of stars and gases. It typically has a large bulge at the center. Arms rotate outward from this central bulge.
The central bulge is thought to contain a supermassive black hole. The stars within the bulge tend to be older than the stars in the spiral arms.
Age and Color
New stars are actively created in the spiral arms of this type of galaxy. This active creation of new stars makes spiral galaxies young galaxies. These galaxies have a bluish color that is given off by young stars.
The earth and our solar system are part of the Milky Way galaxy. The Milky Way is a young spiral galaxy.
Improving Your Reading and Thinking Skills
Think for a few moments. Try to recall the major ideas in this article. When you are done, click the box below for a list of main ideas.
How did you do? With practice, you should be able to identify many of the major ideas. You may even discover some important ideas that aren’t listed.